Electrical heating apparatus



Jan. 25 192 7 e. H. COLLINS ET AL ELECTRICAL HEATING APPARATUS 2 Sheets-Sheeti Filed July 1, 1925 1,615,742 Jan. 25, 1927. G H. COLLINS ET AL ELECTRICAL HEATING APPARATUS Filed July 1925 2 Sheets-Sheet 2 "IIIIIIIIIA'IIIIIII Patented Jan. 25, 1927.

" UNITED STATES PATENT OFFICE.

GEORGE HENRY COLLINS AND HERBERT FRANCIS COLLINS, 0F BIRMINGHAM,

ENGLAND.

ELECTRICAL HEATING APPARATUS.

Application filed July 1, 1925, Serial No. 40,914, and in Great Britain July 8, 1924.

This invention relates to a safety cut-out for\ electrically heated appliances, more particularly forelectric kettles and like liquid heating domestic utensils. \Vith such appliances, if the current is inadvertently left on or turned on when the vessel is empty, overheating quickly occurs and results in serious damage unless means are provided for interrupting the flow of current.

The invention has reference to that class of cut-out in which a movable conductor tends to move so as to break the heating circuit, but is normally retained from so doing by means of a fusible connection which maintains it in fixed relation to a support in thermal connection with a hot part of the apparatus, the fusible connection being made to a member which is readily removable from the apparatus to allow of its being replaced or re-set after fusion has occurred.

With automatic cut-outs of this class as hitherto constructed, it is often found, should the current be inadvertently left on when the vessel is empty, that the rise in temperature is so sudden that damage oc-.

curs before the cut-out has time to operate. A primary aim of the present invention is to provide an improved construction which will provide for a quick and sure working of the cut-out. Particular objects for obtaining this aim are to provide a construction which requires the use of only a small amount of fusible material, and in which the heat from the heating elements of the apparatus travels to said fusible material by an all metal path and is not hindered by insulating media. A further object is to lessen as much as possible the resistance to said flow of heat to the fusible material which occurs at the junction of the fixed support with the detachable or removable member to which the fusible connection is made, by providing a large surface contact between said two members and positioning the fusible material in close juxtaposition to the surfaces of contact.

A further particular object of the present invention is to provide spring operated means for positively moving the movable conductor or bridge away from its complemcntaryfixed contact or contacts.

A still further object of the present invention is to prevent any possibility of the able conductor from contacting with adja-- cent parts of the structure.

The present invention also seeks to provide an improved and simplified construction which, while attaining the above mentioned objects, at the same time enables the cut-out to be easily re-set after fusion by unskilled persons and without the necessity of making a fresh soldered or other fusible connection before the heater can again be put into use.

Referring to the drawings:

Figure 1 is a vertical section through the lower part of a kettle made in accordance with this invention.

Figure 2 is an inverted plan thereof with the undercover and feet removed.

Figure 3 is an enlarged view of part of Figure 1 showing the cut out after release.

igure 4 is a transverse section through the bridge.

Figure 5 is a perspective view of the re movable member and retaining members.

Figure 6 is a similar view of an alternative form of removable member and retaining member.

Figure 7 is'a section on line 77 of Figure 2 showing a pair of insulating devices.

Figure 8 is a plan of a blank forming part of one of said devices, and

Figure 9 is a perspective view showing the blank pressed to shape.

Referring to Figures 1 to 5, the bottom 1 of the kettle has two electric heating elements 2 secured to its underside by means of crossstrips 3 and washers 4 connected with the bottom 1 by means of rivets 5. The sides of the kettle 6 extend downwardly beyond the bottom 1 to engage with the periphery of an under cover 7 which carries feet 8. The under cover 7 is secured in position by means of nuts 9 on the rivets The central part of the end cover 7 is domed or recessed at 10 to provide accommodation for the downwardly extending parts of the cut-out.

, Each of the heating elements 2 has one of its ends connected b a lead 11 t: a plug socket 12 provided on t e edge of the kettle. The other end of each heating element is connected by a lead 13 to a plate 14 which is mounted on the under face of the heating element and is insulated therefrom. These plates 14 are normally connected electrically through the safety cut-out, the two heating .upper part 18 is cylindrical, while a lower part 19 of. the member 17 has sloping sides at 20 and an enlarged portion at 21 pro- .E-led w th a transverse slot at 22 for reeiving a screwdriver. On the external eripher of the upper portion 18 of the emovab e member are soldered two retainrzg '..iemberf' 25 also formed of material nonusi'cle at temperatures attainable by the .pparatus. These retaining members are in the form of segments of a sleeve and are each provided with lugs 26 which enable them to be connected to the removable member by a length of wire 27 which passes through a hoe 28 in the lower end of said member.

A bridge 30, which constitutes a movable contact, is mounted on the upper end of the removable member 17 by means of a boss 31 which has a central opening fitting loosely around the upper portion 18 of the removable member, and is retained in position thereon by engagement with the retaining members 25. The bridge includes a sheet metal member 35 of a resilient nature which has two.upwardly curved arms connected to each other by an intermediate portion which has a large central hole. This intermediate portion of the member 35 is mounted on the boss 31 and insulated therefrom by being clamped between two mica washers 36 retained between a flange 37 and a lock 111g nut 38 on the boss. The boss 31 is recessed at 39 to receive the end of a coiled spring 40 which is located around the stud 15 and bears atits upper end against an enlarged collar 41 on said stud. This spring 40 tends to force the bridge downwardly, but the bridge is retained in position by the engagement of the boss with the retaining members 25, and when in position the ends of the two arms of the member 35 en age with the plates 14, which constitute xed contacts, and establish an electrical connection between them.

In operation, should the current be left on when the kettle is empty, before overheating occurs, heat travels down the stud 15 from the bottom 1 and melts the soldered connection between the retaining member 25 and the removable member 17, thus allowing the spring 40 to slide the bridge down wardly on the upper part of the removable member 17 and thus break the electrical connection between the plates 14. If the kettle is inverted for any reason when the cut-out has fused, the spring will prevent the bridge from falling into contact with the two plates 14.

The curved sides 20 on the lower portion of the removable member 17 prevent any possibility of the retaining members 25 becoming locked in position against the enlarged portion 21 when their soldered connection with the upper portion 18 is fused, while they prevent the bridge'from falling further than is necessary to break the connection between the plates 14. The wire 27 prevents the retaining members 25 from becoming lost or separated from the removable member. In order to reset the cut-out after it has been released, it is only necessary either to replace the removable member 17 with a separate one which has retaining members 25 already soldered thereon, or else to detach the existing removable member from the end of the stud 15 and to resolder its retaining members 25 in position, when it can be again screwed on the stud 15 so that the members 25 will retain the bridge in contact with the plates 14 against the action of the spring 40.

A spare removable member 17 having retaining members 25 already in position may be conveniently located ready for use, if required, on the upper side of the under cover 7, and a spring clip 44 secured to the cover may be provided for maintaining the removable member in position. This part of the kettle is comparatively cool, and consequently the connection between the retaining members 25 and the removable member will not be .iuscd before it is required for use.

In Figure 6, an alternative form of removable member 45 and retaining member 46 is illustrated. In this form the greater part 47 of the removable member 45 is cylindrical, while an enlarged head 48 at the lower end has a screwdriver slot 49 and forms a shoulder at 50. The retaining member 46 is in one piece and in the form of a sleeve, and it is soldered in position near the upper end of the part 47. \Vhen overheating occurs, the retaining member or sleeve 46 moves down until it engages with the shoulments comprise sheets of insulating material upon which the heating wire is wound, and these sheets 55 are sandwiched between the bottom 1 of the kettle and plates 56 which are clam ed in position by the members 4. The p ates 14 are secured to the plates 56 by rivets 57, a sheet of mica 58 being interposed so as to insulate the plates 14 and 56. The plates 14 are provided with large holes, and on one side they are formed with circular recesses 59 around the edges of these holes for accommodating mica washers 60 which are located on the shanks of the rivets. Thus, it will be seen that the edges of the holes in the plates 14 are prevented from coming in contact with the rivets.

In order to prevent the heads 61 of the rivets 57 from accidentally coming into contact with an end of the bridge 30, which might occur when the cut-out has fused, the head of each rivet is effectively insulated by means of a tubular or sleeve-like insulating member 62. This member 62 which is formed from a moulded asbestos compound is adapted to stand high temperatures. One end of the member 62 is provided with a metal washer 63 which has a central hole 64 and a number of peripheral ears or projections 65. The washer 63 is located so thatits face 67 is flush with the end face of the member 62, and the cars are bent out of the plane of the central portion of the washer, as shown in Figure 9, and they are embedded in the tubular member 62.

In securing the plates 14 to the plates 56 the shank of the rivet 57 is passed through the holes 64 in one of the insulating devices, and a sufficient number of mica washers 60 are then placed on the shank to fill the re cesses 59 and also space the metallic end of the insulating device away from the face of the plates 14. The shank of the rivet is then passed through the plates 14 and the sheet of insulating material 58 and the plates 56, and while its end is being riveted over, the force of the blows is taken by any suitable tool inserted in the hollow member 62 so as to contact directly with the head 61 of the rivet. By means of these insulating de-' vices the heads of the rivets 57 are effectively prevented from coming into contact with the bridge 30, and guiding members are provided for correctly positioning the arms of the bridge with respect to the contacts 14 and preventing their engaging with and grounding the circuit to any part of the structure, such, for instance, as the plates 2.

Thus any leakage of the current which might result in giving a shock to anyone us- I ing the kettle is prevented; or, alternatively,

if the heating circuit is grounded to thekettle, any ossibility of a short, circuit occurring is t us avoided.

' What we claim then is i 1. In electrical heating apparatus, a mov able bridge conductor of sheet metal having arms for engagement with a pair of fixed contacts, a metallic bush secured centrally.

of and insulated from the bridge conductor, a fixed stud in thermal connection with a hot part of the apparatus and extending downwardly through the bush, a coil spring located around the stud and tending to force the bush downwardly to disengage the bridge conductor arms from the fixed contacts, a non-fusible elongated nut adapted for screwing on the lower end of the stud and making a sliding engagement within the bush, and-a non-fusible retaining member normally secured on the periphery of the nut by a fusible connection and forming a shoulder for engagement by the lower end of the bush to prevent disengagement of the bridge conductor from the fixed contacts.

2. In electrical heating apparatus, a movable bridge conductor having arms for normal engagement with a pair of fixed contacts to form a closed circuit, insulating members forming guides for correctly positioning the arms of said conductor with respectto the fixed contacts, a s ring tending to move said conductor into t e 0 en position, a non-fusible member detac ably secured to a hot part of the apparatus, a retaining member of non-fusible material normally secured to said detachable member by a fusible connection and retaining the movable conductor in the closed position b engagement with the insulated part, an media for insulating the movable conductor from the retaining member and detachable member.

3. In electrical heating apparatus, a movable bridge conductor having arms for normal engagement with a pair of fixed contacts to form a closed circuit, insulating members forming guides for correctly positioning the arms of said conductor with respect to the fixed contacts, a spring tending to move said conductor into the open position, media for insulating a part of said conductor, a non-fusible member detachably secured to a hot part of the ap aratus; and a retaining member of non-fusi 1e material normally secured to said detachable member by a fusible connection and retaining to the.structure of the apparatus, sheets of insulating material interposed between the fixed contacts and said structure, tubular .moulded members formed of insulating material surrounding the heads of the rivets, said tubular members being secured to the rivets by metal washers provided with ears embedded in the tubular member and holes through which the shanks of the rivets pass, insulating media interposed between the metal washers and the fixed contacts, said tubular members forming guides for correctly positioning the arms of the bridge conductor with respect to the fixed contacts and preventing their engagement with the rivet heads or other grounded part of the structure, a spring tending to move said conductor into the open position, media for insulating a part of said conductor, a nonfusible member detachably secured to a hot part of the apparatus, and a retaining member of non-fusible material normally secured to said detachable member by a fusible connection and retaining the movable conductor in the closed position by engagement with the insulated art, the fusible connection being positione below said conductor and insulating media.

5. In electrical heatin apparatus, a movable bridge conductor 0 sheet metal having arms for engagement with a pair of fixed contacts, a metallic bush secured centrally of and insulated from the bridge conductor, a fixed stud in thermal connection with a hot part of the a paratus and extending downwardly throng the bush,'a coil spring located around the stud and tending to force the bush downwardly to disen age the bridge conductor arms from the xed contacts, a non-fusible elongated nut adapted for screwing on the lower end of the stud and making a slidin engagement with the bush, and a non-fusible retaining member normally secured on the periphery of the nut by a fusible connection and forming a shoulder for engagement by the lower end of the bush to prevent disenga ment of the bridge conductor from the ed contacts, said fusible connection being in close proximity to the engagement of said nut with the stud.

In-witness whereof we afiix our si atures.

GEORGE HENRY COLLI S. HERBERT FRANCIS COLLINS. 

